Process for preparing chlorofluoroethylenes



United States Patent PRQCESS FOR PREPARING CHLOROFLUORO- ETHYLENESMarvin R. Frederick, Brecksviile, Ohio, assignor to The B. F. GoodrichCompany, New York, N. Y., a corporation of New York No Drawing.Application April 8, 1952, Serial No. 281,263

3 Claims. (Cl. 260-653) This invention relates to an improved processfor preparing chlorofiuoroethylenes, and particularly to the preparationof such compounds by dehydrochlorination of chlorofluoroethanes with anaqueous solution of an alkali hydroxide in the presence of asurface-active agent.

Chlorofluoroethylenes such as i H F and C1 F 01 F have been prepared bychemical dehydrochlorination of the appropriate chlorofiuoroethane,using, for instance, an aqueous potassium hydroxide solution containingmethanol. Such processes do not result in optimum yields and undesirableside reactions involving methanol occur. For example,imethoxy-1,1-difluoro-2,2-dichloroethane is an undesirable byproductresulting from the prepararation of dichlorodifiuoroethylene,

by this method.

It is an object of this invention to provide a process for preparingchlorofiuoroethylenes by chemical dehydrochlorination of the appropriatechlorofiuoroethane, wherein undesirable side reactions do not occur.Another object is to attain improved total yields of the desiredproduct. A further object is to obtain faster reaction rates.

I have now discovered that these and other objects are readilyaccomplished by dehydrochlorinating chlorofluoroethanes with a methanolfree aqueous solution of an alkali hydroxide in the presence of asurface-active agent. When proceeding in this manner no undesirable sidereae tions occur, and the reaction, quite unexpectedly, pro- (I ceedsvery smoothly at a much more rapid rate and to a higher yield than isordinarily experienced.

In the preferred practice of my invention a chlorofluoroethane is mixedwith a small amount of a surfaceactive agent and the resulting mixtureis brought into effective contact with, preferably by the slow additionthereto of, a sufficient amount of an aqueous solution of an alkalimetal hydroxide to liberate the chlorofiuoroethylene and neutralize thehydrogen chloride resulting from the dehydrochlorination reaction. Thereaction is preferably carried out at a temperature such that theliberated chlorofiuoroethylene distills off as it is formed and isthereby separated from the reaction mixture in substantially pure form.

About one percent of an oil-soluble surface-active agent dissolved inthe chlorofluoroethane is preferably used, and a slight molar excess ofa water solution of an alkali hy- "ice droxide of about 33 percentconcentration is added to the chlorofluoroethane at a temperature ofabout C. at such a rate as to keep the reaction under control. The orderof addition may be reversed and the chlorofiuoroethane added to thealkali hydroxide solution. When this technique is followed, use of asmall amount of a watersoluble surface-active agent may be desirable.

The chloroiluoroethane preferably employed is1,1-difluoro-1,2,2-trichloroethane which on dehydrochlorination givesl,1-difiuoro-2,2-dichloroethylene. However, there may also be used otherchlorofiuoroethanes containing a hydrogen atom attached to one of thecarbon atoms and a chlorine atom attached to the other carbon atom andotherwise containing, attached to either or both carbons at least oneother chlorine atom and at least one fluorine atom, in which event onemolecule of hydrogen chloride is eliminated with the production of achlorofluoroethylene on suitable treatment. For example,

is prepared from H F 01dd-r a 51 and other ehlorofiuoroethylenes such asare likewise prepared from the appropriate chlorofiuoroethane.

The type of surface-active agent utilized in the practice of thisinvention is not critical and may be any of the anionic, cationic ornon-ionic types described on page 109 of Surface Active Agents by Youngand Coons, and listed between pages 117 and 152 of the same text. Thesur- I face active agents most useful and preferred are the oillecithintype.

I and the amine type agents and their derivatives.

soluble materials. Representative of this class are the aralkylsulfonates such as alkyl naphthalene sulfonate, fatty acid esters suchas sorbitan oleate and glyceryl oleate, andnaturally occurring materialsof the soya bean Water-soluble surface-active agents are useful since aphase inversion often occurs during the course of the reaction.Water-soluble surface-active agents of considerable utility in thisinvention include the salts of alkyl sulfates and sulfonates and theirderivatives Mixtures of oil and water-soluble surface active agents arealso particularly useful. Also useful are the organophilic clays andpolymeric electrolytes.

The amount of surface-active agent preferably used is about one percentbased on the amount of the chlorofluoroethane. One-half percent issatisfactory and even as little as one-tenth percent is operative. Morethan one percent may be used but is generally an unnecessary excess.

The alkali hydroxide solution used to dehydrochlorinate thechlorofiuoroethane is preferably aqueous potassium hydroxide or sodiumhydroxide, although the alkaline earth metal hydroxides may also beused. A slight molar excess of the alkali hydroxide is required toobtain the best yield of desired product, 0.1 mol excess generally beingsufiicient. Concentrations of the alkali hydroxide solutions from 30 to40 percent are the most efiicient for the purposes of this invention.The alkali hydroxide solution is preferably added to the reactionmixture as rapidly as possible while maintaining the reaction undercontrol. As has already been mentioned, the chlorofiuoroethane may beadded to the alkali hydroxide solution but is preferably reacted byadding the alkali hydroxide solution to the chlorofluoroethane.

In carrying out the reaction, the temperature preferred is from 40 to 60C. When dehydrochlorinating 1,1-difluoro-1,2,2-trichloroethane atreaction temperatures below 40 C. the reaction is slow in starting, andat temperatures above 60 C. more difiiculty is experienced in collectingand retaining the volatile l,1-difluoro-2,2-dichloroethylene (B. P. 190.), although this may be adequately handled by proper mechanicaltechniques.

The following examples are given to illustrate applica tions of thisinvention.

I Example I 3729 grams (22 moles) of 1,2,2-trichloro-1,1-difluoroethanecontaining 20 grams (0.5%) of a soya bean lecithin known as Yelkin TT isadded to a liter, 3 neck flask. This reaction vessel is equipped with athermometer' extending into the reaction mixture, a dropping funnel, amechanical stirrer and water cooled reflux condenser with a take ofl?tube attached in such a way that gas from the top of the refluxcondenser will go to a dry ice acetone trap where the product iscollected. The reactor is heated with a Glas-col heating mantle to about50 C. 968 grams (24.2 moles) of sodium hydroxide dissolved in 2 litersof water is added slowly until the reaction starts. When the reactionstarts the l,l-difluoro-'2,2- dichloroethylene distills ofl vigorouslyfrom the reaction mixture. The fiow of waterthrough the reflux condenseris controlled so that the temperature of the eflluent water is 22 to 25C. The reaction temperature is maintained from 45 to 60 C. The alkalihydroxide solution addition requires about 2 hours. The distillation ofproduct from the reaction mixture into the receiver is usually completedbefore all of the alkali hydroxide solution is added. The reactionproduct, 1,l-difluoro-2,2-dichloroethylene is washed with ice water.Because of the volatile nature of the monomer, care must be taken toavoid evaporation losses. The monomer is decanted from the wash waterand distilled through a 1-inch diameter column of 6 to 8 inches of4-mesh anhydrous calcium chloride and 20 inches of A1 inch glasshelices. 2623 grams (19.7 moles) of 1,1-difluoro-2,2-dichloroethylene,boiling point 1921 C. is obtained. This represents a yield of 97percent.

- This result may be compared to those obtained by treating1,1-difluoro-1,2,2-trichloroethane with an aqueous solution of potassiumhydroxide containing methanol at 50-60 C., in which reaction times ofthree to eight hours, yields of 85 to 75 percent and some 1-methoxy-1,1-difluoro-2,2-dichloroethane as an undesirable lay-product are obtained.

Example 2 Using essentially the same procedure outlined in Example l,but with 0.5 percent alkyl naphthalene sulfonate Example 3 Usingessentially the same procedure outlined in Example 1, one percent ofsoya bean lecithin is dissolved in l,2-dichloro-2,2-difluoroethane andthe mixture treated at about 50 C. with a slight molar excess of a 30percent solution of sodium hydroxide. l.-chloro-2,Z-difluoroethylene ingood yield is obtained.

The examples given hereinbefore are only illustrative embodiments of myinvention, and I do not desire or intend to be limited solely thereto,but only as required by the spirit and scope of the appended claims.

I claim:

1. The process for preparing l,1-difluoro-2,2-dichloroethylene froml,l-difl.uoro-1,2,2-trichloroethane which comprises reactingl,l-difluoro-1,2,2-trichloroethane with an excess of an alkali hydroxidein aqueous solution in the presence of a small amount of an oil-solublesurfaceactive agent selected from the class consisting of aralkylsulfonates and soya bean lecithins.

2. The process for preparing 1,l-difluoro-2,2-dichloroethylene froml,1-difluoro-l,2,2-trichloroethane which comprises reacting1,1-difluoro-l,2,2-trichloroethane with 0.1 molar excess of sodiumhydroxide in 30 to 40 percent aqueous solution in the presence of about1 percent of soya bean lecithin, calculated on the weight ofdifluorotrichloroethane utilized, at a temperature of 40 to C., andcollecting by condensation the liberated difluorodichloroethylene.

3. The process for preparing 1,1-difluoro-2,2-dichloroethylene froml,l-difiuoro-1,2,2-trichloroethane which comprises reactingl,l-difluoro-1,2,2-trichloroethane with about 0.1 molar excess of sodiumhydroxide in 30 to 40 percent aqueous solution in the presence of about1 percent alkyl naphthalene sulfonate, calculated on the weight ofdifiuorotrichloroethane utilized, at a temperature of 40 to 60 C., andcollecting by condensation the liberated difluorodichloroethylene.

References Cited in the file of this patent UNITED STATES PATENTS2,322,258 Strosacker et al June 22, 1943 2,566,807 Padbury et al Sept.4, 1951 OTHER REFERENCES Handbook of Chemistry and Physics, 30th ed.,page 1720 (1947).

Schwartz et al.: Surface Active Agents, pages 205-6 (1949).

1. THE PROCESS FOR PREPARING 1,1-DUFLUORO-2,2-DICHLOROETHYLENE FROM1,1-DIFLUORO-1,2,2-TRICHLOROETHANE WHICH COMPRISES REACTING1,1-DIFLUORO-1,2,2-TRICHLOROETHANE WITH AN EXCESS OF AN ALKALI HYDROXIDEIN AQUEOUS SOLUTION IN THE PRESENCE OF A SMALL AMOUNT OF AN OIL-SOLUBLESURFACEACTIVE AGENT SELECTED FROM THE CLASS CONSISTING OF ARALKLYSULFONATES AND SOYA BEAN LECITHINS.